The present invention relates to games of chance. In particular, it relates to a method of configuring a reel-slot game to achieve a desired probability of occurrence of certain game outcomes. This application has been filed concurrently with and on the same date as my related application for Method and Apparatus for Configuring a Video Output Gaming Device, whose disclosure is incorporated by reference.
Reel-slot machines are among the most popular wagering devices in the United States at this time. A typical mechanical slot machine is a three reel device, that is configured to randomly display three symbols on one or more pay lines from a number of symbol bearing reels.
With conventional mechanical reel-slot machines, the probability of occurrence of any particular three symbol game outcome is dictated by the game designer's choice of symbols, the number of reels, the number of positions on each reel and the number of times each symbol appears on each reel.
The frequency of occurrence, or "hit frequency" of each possible outcome, in combination with the percentage of coins dropped, or "hold" are considered in defining one or more pay tables for a given game. The physical configuration of a typical mechanical reel-slot machine therefore imposes a practical limit on the maximum payout on mechanical reel slot machine outcomes.
Game designers have been presented with the challenge of designing reel-slot games that permit symbol combinations with a hit frequency low enough to raise the value of the prize. Higher payouts are desirable because they are believed to attract more players to the game. Machines that pay higher payouts are also thought to attract additional players, namely those interested in betting on a long shot. Conventional mechanical reel-slot machines cannot be configured to provide opportunities for earning larger payouts, such as progressive payouts because of the physical limitations described above.
The minimum probability of a payout for conventional slot machines is 1 in N raised to the power R, where N is the number of angular rotational positions on each reel and R is the number of reels. The lowest probability that can be offered on a three reel, twenty reel stop position per reel machine would therefore be 1 in 8000 (20 to the third power).
Game designers have attempted to overcome the physical limitations of standard reel-slot machines on pay tables by designing games with additional and bigger reels. Additional and larger reels permit a larger number of symbol combinations and therefore increase the size of the prize for certain winning combinations.
Larger reel machines have not been well accepted by casino patrons. The larger machines are perceived as having less favorable odds of achieving winning symbol combinations. The mechanical equipment used to physically stop and lock the reels in a conventional reel-slot machine can also wear out and produce outcomes that are not purely random.
Electromechanical reel-slot machines have been introduced in an attempt to improve the reliability of conventional reel-slot machines. Electromechanical reel-slot machines are equipped with random number generators which select numbers assigned to each angular position on the reel. Electromechanical reel-slot machines include a device to stop the reel at the selected angular position. However, these machines still have the physical size and configuration which limits the size of the prize and the hit frequencies.
The inherent payout limitations of mechanical and electromechanical reel-slot machines have been overcome in part by offering machines configured according to a method disclosed in Telnaes U.S. Pat. No. 4,448,419.
Telnaes describes a method of providing payout odds which are independent of the hit frequencies determined by the geometry of a reel-slot machine. "Virtual" addresses are provided on one or more reels. For example, in a twenty reel stop position reel, position 19 may be assigned random numbers 1 and 21. When the random number generator selects 21, for example, a microprocessor instructs the device to display the symbol assigned to "virtual" stop 21. The microprocessor then instructs the reel to stop at a reel stop position bearing a symbol that matches the symbol assigned to virtual stop 21. This position need not be position 19.
This technology advantageously allows the game designer to define the probability of occurrence of a selected symbol that is different from a conventional three reel-slot machine. For example, a cherry symbol might be present on only one out of twenty reel stop positions, with a probability of occurrence of 1/20 or 0.05 for a cherry on that particular reel. By providing, for example, a reel with 60 "virtual" reel positions, and by assigning a cherry symbol to two of the addresses, the odds of the cherry appearing on the same reel can be changed from 1 in 20 (0.05) to 2 in 60 or (0.0333).
Although this technology is a vast improvement over conventional reel-slot devices, it still possesses certain disadvantages. The random number generator selects numbers corresponding to "virtual" stop positions on each reel independently of the other reels. Utilizing the Telnaes technology, the game designer is able to modify the probability of occurrence of certain game symbols, but the probability of occurrence of all possible game outcomes is completely dependent upon the selected number of reels, the number of virtual reel positions and the symbols assigned to each virtual reel position. In other words, the probability of occurrence of all possible game outcomes, including game outcomes requiring certain symbols to appear in a predetermined order on the pay line (hereinafter referred to as a "positional win") and consequently payoffs cannot independently be assigned their own probability of occurrence practicing this method. For this reason, Telnaes does not provide the game designer with enough flexibility in determining the frequency of occurrence of certain combinations of symbols. For example, if a positional win consisting of Cherry, Double Bar and Double Bar, in that order, is designated as the highest winning combination, under Telnaes, it might not be possible to offer other combinations with a cherry symbol appearing in a lower ranked combination because the probabilities of occurrence of the cherry in the first position in the different outcomes does not coincide with the probability needed to cause the cherry to appear frequently enough in other outcomes.
Nicastro et al. U.S. Pat. No. 5,569,084 describes a method of selecting a probability of occurrence of selected symbol combinations in a reel-slot game. According to a first example of the Nicastro method, all possible game outcomes (symbol combinations) are first defined. Each outcome is assigned to a position on a "branching tree" stored in ROM memory. The branching tree includes a main tier, branching tiers and terminal nodes. In the first example, each possible outcome is assigned to a terminal node. Each branching tier is assigned a probability of occurrence. This probability, along with the number of terminal nodes assigned to the branching tier determines the probability of occurrence of the symbol combination assigned to the terminal node. By selecting the position of each outcome on the branching tree, and the number of terminal nodes, if any, the probability of occurrence of each outcome is defined.
The Nicastro method identifies all possible outcomes, then assigns a probability of occurrence to each outcome. This in turn defines the relative probability of occurrence of each game symbol. The Nicastro method does not randomly and independently select each symbol on the pay line. Nor does this method teach that it would be desirable to randomly and independently select each symbol on the pay line.
In a second example illustrated in Nicastro, a single symbol is assigned to each terminal node, and then a random number generator selects a terminal node for each symbol selected. The symbols are independently and randomly selected. In this example, the method does not permit the game designer to assign a probability of occurrence to certain symbol combinations independently of assigning a probability of occurrence to the individual symbols.
Durham U.S. Pat. No. 5,456,465 describes a method for operating a microprocessor based reel-slot machine. According to the method described by Durham, all possible symbol combinations in a reel-slot game are defined, and assigned a payout value. A random number generator selects a first multiplier number, and then a second multiplier number. The numbers are multiplied to arrive at a payout value. A random number generator then selects a single symbol combination from the set of symbol combinations assigned that particular payout value. The symbols are then displayed on the pay line. According to the method described by Durham, all game outcomes are preselected, and are then assigned a payout value. The Durham method does not describe a method of randomly and independently selecting each symbol in an outcome.
The Durham and Nicastro (first example) methods utilize different techniques for assigning a probability of occurrence to a set of preselected game outcomes. Telnaes and Nicastro (second example) do not teach a method of assigning probabilities of occurrence to certain game outcomes independently of assigning a probability of occurrence to individual symbols. The probability of occurrence of game outcomes according to Telnaes and Nicastro (second example) cannot be "tuned" independently of the probability of occurrence of each game symbol.
It would be desirable to combine the ability to randomly select each symbol appearing on the pay line based on the assigned relative probability of occurrence of each game symbol and at the same time assign a probability of occurrence to certain categories of game outcomes. It would also be desirable to provide a method of configuring a gaming device having a preselected number of game outcome templates, whose game outcome templates can be assigned a probability of occurrence independently of the assigned probability of occurrence of the individual game symbols used to fill the template. It would also be desirable to define a game utilizing the method of the present invention to display all of or fewer than all possible outcomes.